In tilt sash window systems, it is advantageous to have sash pins that lock within sash shoes when window sash are untilted. Accidental withdrawal of untilted sash pins from counterbalanced shoes can cause several problems, depending on the operation of the shoes. Accidental sash pin withdrawal is also not uncommon. A reason for this is that when assembled windows are carried around construction sites before installation in a building, they are often carried by frame side or stile members, which can bow the frame sides and extract the sash pins from the sash shoes. A term that summarizes the problem of accidentally withdrawing sash pins from shoes and refers to the way windows are usually carried about construction sites is "suitcasing".
For shoes that do not automatically lock when sash pins are accidentally extracted, pulling sash pins out of sash shoes by suitcasing sends the shoes flying like projectiles within the window jambs, under the force of counterbalance springs attached to the shoes; and this can break counterbalance components and require at least reassembling and possibly rebuilding the window. Some shoes lock automatically if a sash pin is withdrawn; but problems can still occur by pulling sash pins out of sash shoes, even if the shoes lock in place. Once pulled from shoes, the sash pins may not go back into proper position; and reconnecting the pins properly with the shoes can cause problems at a construction site. The sash pins could end up pressing against the sash shoes in positions where they are unable to enter the shoes, for example; or the sash pins could end up underneath the shoes instead of properly positioned above the bottom of the shoes. Either of these problems can lead to frustration, lost time, and possible breakage of components.
U.S. Pat. Nos. 4,930,254 and 5,069,001 address this problem with sash pins that interlock with window jambs when the sash are untilted. This requires specially constructed jambs and sash shoes, however, to provide an operating space for the lock elements extending laterally from the sash pins.